The present invention is directed to strengthened pipe fittings and a method for making strengthened pipe fittings.
Pipe fittings and, more specifically, hollow, tubular shaped pipe fittings having connector ends with either internal taper threads (commonly referred to as female pipe threads) or external taper threads (commonly referred to as male pipe threads) are commonly used in the plumbing and hardware industry. Typically, male pipe threads of a pipe fitting are threaded into female pipe threads in a second pipe fitting to form a pipe joint. The pipe joint relies upon the wedging action of the oppositely tapered male and female pipe threads to seal the pipe joint. In operation, the wedging action between the male and female pipe threads causes the pipe fitting with the male pipe threads to compress and the pipe fitting with the female pipe threads to expand. However, the wedging action can cause structural failure of the female pipe fitting during joint make-up if the pipe joint is overtightened or stress fatigue failure of the female pipe fitting over time, since the tubular shape of the pipe fitting is more susceptible to expansion than compression.
Pipe fittings made of plastic with female pipe threads are particularly susceptible to structural failure. These plastic pipe fittings can fail prior to obtaining a pressure-tight seal at the pipe joint. Thus, an entire pipe system may have to be derated as a result of the weakened plastic pipe joint.
The prior art has attempted to solve this problem by placing a reinforcement band around the outside of the female pipe fitting to restrict and/or inhibit expansion and splitting of the pipe fitting. However, this method has proved not to be satisfactory.
Accordingly, there is a need for strengthened pipe fittings with female pipe threads and a method for making pipe fittings with female pipe threads which (i) withstand deformation produced during joint make-up, overtightening of the pipe joint and stress fatigue failure over time, and (ii) allow for the use of plastic pipe fittings without the need for pressure derating in the pipe system.